1. Field of the Invention
The present invention relates to a method and apparatus for fixation, stabilization and fusion of the human occipitocervical junction.
2. Description of the Related Technology
The normal range of motion of the craniospinal junction includes 27° of flexion and extension, and 90° of lateral rotation; the craniospinal junction is thus the most mobile and articulatable part of the human body. It is also the most active part of the human body in movement throughout the day, typically performing greater than 3 million motions a year. The craniospinal junction transmits the entire nervous structure to the body (with the exception of the vagus nerve), and is thus unfortunately susceptible to a host of degenerative disorders. Emblematic of these is rheumatoid arthritis, a chronic degenerative condition that arises in 2% of the population, causing predictable changes in the joints and bone structure of the cervical spine, often including vertical migration of the odontoid and trauma to the ligamentous structures of the craniocervical junction.
25% of rheumatoid arthritis sufferers develop atlantoaxial subluxation and 9% develop basilar invagination. Clinically these patients invariably experience severe neck pain and neurological deficits, including weakness and sensory loss. Untreated, patients suffer progressive decline, losing the ability to walk. The untreated patient with myelopathy due to compression of the spinal cord has a 50% likelihood of dying within 1 year. Surgical intervention is therefore necessary to stabilize the craniocervical junction, restore neurologic function and prevent further neurologic deterioration. However, occipitocervical stabilization in rheumatoid arthritis can be especially challenging because of such factors as poor bone quality, poor nutritional status and long term steroid use.
There are also other common causes of cranio-cervical instability, including traumatic fractures, which can include approximately 3,000 fractures of the upper spine related to head trauma each year; congenital diseases, including Down's, Morquio's and spondyloepiphyseal dysplasia syndromes, with a prevalence of at least 50,000; osteogenesis imperfecta, with a prevalence of 7,000 patients; cancer, with about 1000 cases per year; and numerous causes of bone softening. Tumors and infections may also cause destruction of the stabilizing elements.
However, the largest group of patients suffering from poor craniocervical stabilization lies in the pediatric group amongst a large group of children who have been misdiagnosed with neuropsychiatric disorders, such as Asperger's Syndrome, autism, Attention Deficit Hyperactivity Disorder and forms of dyslexia who harbor underlying disorders of the brainstem and spinal cord which result from subtle and sometimes gross anomalies which result in mechanical deformation and abnormal stresses of the neuraxis at the craniocervical junction. Various disorders have been found to frequently result in chronic and subtle neurological changes: retroflexion of the odontoid, platybasia, non-traditional forms of basilar invagination and an abnormal clivo-axial angle, which can result in deformity of the brainstem and upper spinal cord.
The clivioaxial angle is depicted in FIG. 1, while an example of basilar invagination is depicted in the image that is shown in FIG. 2, with compression to the brainstem being clearly visible. These conditions have been reported to cause such symptoms as sleep apnea, delayed speech, gastroesophageal reflux, and altered behavior such as attention deficit disorder, headaches, and a myriad of other sensori-motor syndromes. The ubiquity of craniospinal junction pathology has only recently been appreciated.
Hitherto, patients undergoing craniospinal stabilization have required an arduous surgery and recovery. Some patients undergo a decompressive surgery from the front of the neck (transoral resection of the uppermost part of the spine), followed by fusion in the back of the neck, and followed by 3 months of stabilization in a halo brace, which encompasses the head (held by 4 screws in the skull) and the upper body.
Numerous fixation devices have been described such as those that are disclosed in U.S. Pat. Nos. 5,030,220; 5,034,011; 5,545,164; 5,507,745; 6,547,790; 6,524,315; 6,902,565 B2 and U.S. Published Patent Applications US2005/0288669 A1; US2005/0283153 A1 and US2005/0080417 A1, all of which are hereby incorporated by reference as if set forth fully herein.
A need exists for a system and methodology that accomplishes the goals of reduction of deformity, successful immobilization and fusion of the craniospinal junction, in a shortened surgery, thereby allowing the patient to return to a normal quality of life within a short period of time.